A. Field of the Invention
The present invention relates to an endoscope having a distal structure fitted with a solid-state image sensing device, such as an SID.
B. Description of the Prior Art
Among prior art endoscopes adapted for observation in a body cavity, an improved endoscope is disclosed in Japanese Patent Disclosure (Kokai) No. 60-241010, for example. This endoscope has a distal structure which is fitted with a solid-state image sensing device, such as an SID.
In such a conventional endoscope, the image sensing device is situated on a plane which contains the longitudinal axis of the distal structure of an insertion section. An objective optical system is disposed in one of the upper and lower spaces of the image sensing device, while a forceps channel is located in the other. A prism is attached to an end portion of the optical system. It serves to totally reflect a light incident on the optical system, at right angles, thereby guiding the light to the image sensing device.
In the endoscope whose solid-state image sensing device is situated on the plane containing the longitudinal axis of the distal structure, as described above, the objective optical system, a light guide, the forceps channel, and an air-water feed channel must be housed within a space which is restricted to the upper and lower portions of the image sensing device. However, the space inside the distal structure is limited, depending on the heights of the optical system and the prism, the thicknesses of the image sensing device and a substrate, the thicknesses of various channels, and the locations of the various members. If a relatively thick forceps channel is to be disposed in the limited space, the outside diameter of the distal structure must be increased.
Thus, in conventional endoscopes, the arrangement of a relatively thick forceps channel in the insertion section, for the use of various medical instruments, is not compatible with the use of a thinner distal structure of the insertion section, which is required to avoid excessive pain for the patient.